Major goals are to determine: A. Chromophore for synergistic killing by hydrogen peroxide and near-ultraviolet radiation. B. Target of this action (i.e., the specific damage to DNA, protein, etc.) C. Chemistry involved from time that chromophore is afflicted with near-ultraviolet radiation and the final steps leading to death or mutation of the cell. Our current research has given us a number of promising leads: A. Damage may cause a DNA-protein crosslink. To resolve this, T7 phage will be doubly labeled with 3H and 14C and the phage will be purified. Upon dissociation of the protein from the DNA, we should determine whether the near-ultraviolet radiation has caused a crosslink by determining the pattern of separation in cesium chloride equilibrium density gradients. Experiments include: (1) action spectrum analysis; (2) determination of which amino acids crosslink with DNA. B. Preliminary experiments indicate that superoxide anion is produced by near-ultraviolet radiation plus H2O2, and this may be the specific cause of death and mutation in cells. Critical experiments should prove this point and eliminate other possibilities (such as hydroxy radical) as the damaging agent.